1. Field of the Invention
The present invention relates to an engine mount for use in a motor vehicle such as an automobile.
2. Description of the Related Art
Motor vehicles such as automobiles give poor riding comfort when muffled sound is produced in the passenger compartment or the power plant resonates upon vibration of the engine. It has been customary to support the engine on a vehicle frame through resilient engine mounts in order to prevent the engine vibrations from being transmitted to the vehicle body.
The engine mounts have a relatively low spring rate to reduce muffled sound that is produced in the passenger compartment by engine vibrations at a high frequency ranging from 50 to 500 Hz with a small amplitude of .+-.0.05 mm, and a relatively high spring rate to improve poor riding comfort that is developed by engine vibrations at a low frequency ranging from 5 to 50 Hz with a large amplitude of .+-.1.0 mm.
The conventional engine mounts are designed to dampen only vertical vibrations, and hence suffer performance limitations. Specifically, if the vertical spring rate of an engine mount is lowered to minimize muffled sound in the passenger compartment, then the damping force of the engine mount is reduced accordingly, resulting in impaired riding comfort. Conversely, if the vertical spring rate of the engine mount is increased, then the passenger compartment is filled with more muffled sound.
In order to lower muffled sound in the passenger compartment, it would be possible to lower a lateral static spring rate for thereby reducing a lateral dynamic spring rate. According to such a solution, since the lateral static spring rate would be lowered in consideration of the lateral dynamic spring rate, it would not be considered and determined solely for itself. While the engine mount thus designed signed would be effective to reduce muffled sound in the passenger compartment, its rigidity for supporting the power plant would be lowered, making the riding comfort poor.